Hot and steamy: outbreak of Bacillus cereus in Singapore associated with construction work and laundry practices

Abstract

A sudden increase in invasive infections caused by Bacillus cereus group organisms prompted an investigation at the National University Hospital in Singapore. To describe the investigation and management and subsequent difficulties controlling the outbreak. Clinical case reviews were performed on all patients with B.cereus group recovered from clinical samples. Widespread environmental sampling was performed followed by review of hospital ventilation systems, domestic cleaning and laundry practices. B.cereus was recovered from 171 patients during a six-month period coinciding with large-scale construction work beside the hospital. Most patients presented with bacteraemia (146/171; 85.4%) with 46/171 (26.9%) requiring extended treatment courses with vancomycin or other interventions. Sampling confirmed extensive airborne dispersal inside the hospital, including isolation rooms and air-conditioned wards. Hospital linen was heavily contaminated [7403cfu/cm(2); 95% confidence interval (CI): 6349-8457; for 30 towels sampled], encouraged by inappropriate storage in airtight plastic bags (4437cfu/cm(2); CI: 3125-5750) compared with storage in porous canvas bags (166cfu/cm(2); CI: 76-256; P<0.001). Interventions introduced included revision of laundry practices, transport and storage of hospital linen and towels; bleach-based environmental cleaning; and upgrading of ventilation systems throughout the hospital. Clinical case numbers returned to baseline levels within three months, only to rise again following relaxation of laundry practices. Construction work beside this Singapore hospital encouraged heavy contamination of air and environment with Bacillus spp., assumed to be responsible for the outbreak described. Failure to maintain revised laundry practices allowed resurgence of clinical cases, particularly among immunocompromised patients.